Showing papers on "Solitary tract published in 1982"

Amygdaloid and basal forebrain direct connections with the nucleus of the solitary tract and the dorsal motor nucleus

Abstract: Although the amygdala complex has long been known to exert a profound influence on cardiovascular activity, the neuronal and connectional substrate mediating these influences remains unclear. This paper describes a direct amygdaloid projection to medullary sensory and motor structures involved in cardiovascular regulation, the nucleus of the solitary tract (NTS) and the dorsal motor nucleus (DVN), by the use of autoradiographic anterograde transport and retrograde horseradish peroxidase (HRP) techniques in rabbits. Since all of these structures are highly heterogeneous structurally and functionally, details of the specific areas of the neuronal origin and efferent distribution of the projection were examined in relation to these features and with reference to a cytoarchitecture description of the relevant forebrain regions in the rabbit. Amygdaloid projections to the NTS and DVN, as determined from HRP experiments, arise from an extensive population of neurons concentrated exclusively within the ipsilateral central nucleus and confined to and distributed throughout a large medial subdivision of this nucleus. Projection neurons, however, also distribute without apparent interruption beyond the amygdala dorsomedially into the sublenticular substantia innominata and the lateral part of the bed nucleus of the stria terminalis and thus delineate a single entity of possible anatomical unity across all three structures, extending rostrocaudally within the basal forebrain as a diagonal band. Descending central nucleus connections, based upon autoradiographic experiments, project heavily and extensively to both the NTS and the DVN. Within both nuclei, the projections have a highly specific distribution pattern, appearing to correspond largely to structural subdivisions, including the dorsomedial, medial, ventrolateral, ventral, and commissural NTS, and to cell group “a,” a caudally located dorsomedial region, and peripheral regions of the DVN, some of which appear to be involved in cardiovascular regulation. The existence of such an extensive projection system connecting these specific regions is significant evidence in support to its potential for participation in the amygdaloid expression of cardiovascular influences and has important implications for the cellular analysis of the functional role of these influences.

The central projections of the trigeminal, facial, glossopharyngeal and vagus nerves: an autoradiographic study in the rat.

Abstract: The central distributions of primary afferent axons in the facial, trigeminal (mandibular branch), glossopharyngeal, and vagal nerves of the rat have been re-examined using the autoradiographic tracing technique after injections of [3H]proline or [3H]leucine into their peripheral ganglia. Within the nucleus of the solitary tract (NST), the labeled terminals from VII, V, IX and X form a continuous distribution that spans the length of this nucleus. Sensory axons in VII terminate mainly within the lateral division of the rostral NST, although some of the terminals extend further caudally within the nucleus. Immediately caudal to the rostral NST, the distribution continues with major contributions from V and IX. Both are confined mainly to the lateral division of the NST, although some of the fibers in IX terminate within the medial division. Injections into the inferior ganglion of X confirm the extensive distribution of vagal axons as they ramify significantly within the lateral division, and virtually monopolize the medial division of the NST. Thus, the major zone of convergency for these 4 cranial nerves is the lateral division of the nucleus from the level of the entering fascicles of IX caudally to the level of the area postrema. Furthermore, only X has a crossed projection as vagal axons invade the commissural nucleus and the medial division of the contralateral NST. Vagal fibers also enter the area postrema bilaterally. Finally, some afferent fibers from VII, IX and X descend in the dorsal part of the spinal trigeminal tract and terminate within the marginal subdivision of the spinal trigeminal nucleus pars caudalis, as well as the dorsal horn of the cervical spinal cord.

Afferent connections of the cerebellum in various types of reptiles

Abstract: The origin of cerebellar afferents was studied in various types of reptiles, viz., the turtles Pseudemys scripta elegans and Testudo hermanni, the lizard Varanus exanthematicus, and the snake Python regius, with retrograde tracers (the enzyme horseradish peroxidase and the fluorescent tracer “Fast Blue”). Projections to the cerebellum were demonstrated from the nucleus of the basal optic root, the interstitial nucleus of the fasciculus longitudinalis medialis, the vestibular ganglion, and the vestibular nuclear complex, two somatosensory nuclei, viz., the descending nucleus of the trigeminal nerve and the nucleus of the dorsal funiculus, the nucleus of the solitary tract, the reticular formation, and throughout the spinal cord. A distinct bilateral projection to the cerebellum was found to arise in a nucleus previously called nucleus parvocellularis medialis (Ebbesson, ′67). In the present study this cell mass is termed the perihypoglossal nuclear complex, considering its comparable position and fiber connections to the perihypoglossal nuclei in mammals. In all reptilian species studied a contralateral cerebellar projection of a cell mass located in the caudal brainstem adjacent to the nucleus raphes inferior was observed. It seems likely that this cell mass represents the reptilian homologue of the mammalian inferior olive. Most of the spinocerebellar fibers appeared to arise in neurons located in area VII-VIII of the gray matter. In this respect the origin of the spinocerebellar projection in reptiles resembles the origin of the rostral and ventral spinocerebellar tracts in mammals. No indications for the existence of a column of Clarke or a central cervical nucleus in the reptilian spinal cord were obtained. On comparison of the cerebellar afferents in reptiles with the known connections of the cerebellum in amphibians, birds, and mammals, a basic pattern of cerebellar afferent projections appears to exist in these vertebrateclasses, including retinal, vestibular, precerebellar, somatosensory, and spinal afferents.

The ultrastructural localization of serotonin immunoreactivity within the nucleus of the solitary tract of the cat

Abstract: Using a modification of the peroxidase-antiperoxidase technique, serotonin immunoreactivity was localized at the ultrastructural level in the nucleus of the solitary tract of the cat Structures containing serotonin immunoreactivity included unmyelinated axons, varicosities (05 to 2 micrometers in diameter), and synaptic terminals The serotonin-containing synaptic terminals were found less frequently than axons or varicosities Within unmyelinated axons and varicosities, the immunoreactivity was associated mainly with large granular vesicles (80 to 150 nm) While large granular vesicles were found in all immunoreactive structures, greater numbers were observed in axons and nonsynaptic varicosities Serial sections of several nonsynaptic serotonin-immunoreactive varicosities indicated the lack of synaptic specializations associated with these structures In a typical section, only one or two granular vesicles were in synaptic terminals which contained numerous small clear vesicles Serotonin-immunoreactive terminals formed asymmetrical contacts with dendrites and spines No synaptic contacts involving immunoreactive terminals were found on cell bodies or other axonal structures Serotonin-containing neuronal perikarya within the nucleus of the solitary tract were never observed The abundance of nonsynaptic varicosities containing large granular vesicles suggests a possible neurohumoral role for serotonin within the feline nucleus of the solitary tract This is discussed in relation to previous reports concerning the paucity of genuine synaptic contacts involving serotonin in other regions of the central nervous system The presence of serotonin-immunoreactive terminals in the nucleus of the solitary tract also suggests its function as a putative neurotransmitter

Afferent connections of physiologically identified neuronal complexes in the paraventricular nucleus of conscious Pekin ducks involved in regulation of salt- and water-balance.

Abstract: The afferent connections of the paraventricular nucleus (PVN) of the domestic mallard (Pekin duck), Anas platyrhynchos, were demonstrated by means of microiontophoretic injection of horseradish peroxidase (HRP). To place the HRP injection exactly into the PVN, its location was identified prior to the injection by observing antidiuretic reactions to electrostimulations within the rostral hypothalamus of conscious, hydrated animals. Antidiuresis was induced only when electrostimulation was applied to a distinct hypothalamic area. Two different patterns of antidiuresis were observed: (i) an immediate reduction in rate of production of urine, and (ii) antidiuresis preceded by a period of increase in production of urine. Repeated stimulation of the same site with the same parameters resulted in decreasing antidiuretic effects. At the site where stimulation had elicited the most pronounced antidiuresis of either response type, HRP was injected microiontophoretically. Histological examination after 3–8 days of survival revealed delicate injection sites located exclusively in the periventricular portion of the PVN. Adjacent to the dorsal portion of the PVN retrogradely labeled tanycytes and intraependymal neurons were scattered in the ventricular wall. As demonstrated in neurohistological and electron-microscopic investigations, this ependymal region exhibits a particular arrangement of tanycytes and small neurons (10–15 μm in diameter), some of which belong to the neurosecretory type. Additional HRP-labeled neuronal perikarya afferent to the PVN were demonstrated in the contralateral PVN, and on the ipsilateral side in the lateral septum, lateral hypothalamic area and locus coeruleus. Within the nuclei of the solitary tract, stained nerve cells were found ipsilateral as well as contralateral to the injection site. Several of the neurons demonstrated may be considered as candidates for the transmission of signals originating from various receptive structures relevant for the control of avian salt- and water-balance. The physiological results conform to the concept that neurons of the PVN influence urine formation by controlling the release of arginine-vasotocin (AVT). Evidence that suggests additional modes of control exerted by these neurons in salt- and water-balance is presented.

The motor nuclei and primary projections of the facial nerve in the monitor lizard Varanus exanthematicus

Abstract: The location of the motor nuclei and the projection of the primary afferent fibers of the facial nerve of the reptile Varanus exanthematicus were studied by means of the HRP method and the anterograde degeneration technique. The motor nuclei are located ventrolaterally in the rhombencephalon and are constituted by a medial cell group consisting of large, polygonal cells and a lateral cell group consisting of medium-sized, spindleshaped, and multipolar cells. From HRP applications to the various branches of the facial nerve it could be concluded that the medial cell group represents the branchiomotor nucleus and the lateral cell group the superior salivatory nucleus. The efferent axons from the motor nuclei course dorsomedially toward the fourth ventricle, where they form a genu, and exit from the brainstem in the ventral fiber bundle of the facial nerve. The primary afferent fibers enter the brainstem in the dorsal bundle ofthe facial nerve. This bundle courses medially, enters the solitary tract, and diverges into rostrally and caudally running fibers. Part of the caudally directed fibers leave the solitary tract and course laterally toward the descending trigeminal tract. Some fibers enter the nucleus of this tract. There was no noticeable terminal degeneration in the solitary tract or in the descending trigeminal tract or its nucleus.

Central alpha-adrenoceptors involved in cardiovascular regulation.

Abstract: It appears to be established that the central alpha-adrenoceptors involved in the control of cardiovascular function belong to the alpha 2-subtype. They are stimulated by catecholamines, clonidine, and other imidazoline derivatives but also by compounds of rather heterogenous structure. Activation of these central alpha 2-adrenoceptors results in an increase of cardiac vagal tone as well as in decreases of sympathetic nervous activity, blood pressure, and heart rate. alpha 2-Adrenoceptors in the nucleus of the solitary tract appear to be the main site of action of clonidine, followed, in decreasing order of likelihood, by those in the intermediolateral cell column of the spinal cord and the anterior hypothalamus. The location of the alpha 2-adrenoceptors relative to synapses is controversial. Two possibilities have so far been discussed: a location at the terminals of adrenergic neurons (presynaptic) or on the cell bodies or dendrites of not yet identified neurons innervated by adrenergic neurons (postsynaptic). In this paper, attention is drawn to another possibility suggesting a location at the terminals of nonadrenergic neurons.

Chemical stimulation of the nucleus of the solitary tract and the resulting blood pressure response.

Abstract: The cardiovascular effects of catecholamines and related substances after local application into the nucleus tractus solitarii (NTS) of the medulla oblongata of urethane anesthetized rats are summarized. The catecholamines in the nanomolar dose range appear to activate stereospecifically receptor sites in the NTS, resulting in a decrease in blood pressure. Bradycardia occurs after bilateral administration of higher doses. The type of catecholaminergic receptors involved is discussed on the basis of the effects of different catecholamine receptor stimulating agents and pharmacological blockade. Both alpha-methylnoradrenaline and alpha-methyladrenaline are active and it is concluded that they both may contribute to the antihypertensive action of alpha-methyldopa. It is probable that an alpha-type of receptor mediates these hypotensive effects in the NTS. The nature of this receptor needs further characterization.